Lithium ion batteries, nickel hydrogen batteries and other secondary batteries have become increasingly important in recent years as vehicle-mounted power supplies or as power supplies of personal computers and portable devices. In particular, lithium secondary batteries, which are lightweight and allow the obtaining of high energy density, are expected to be preferably used as vehicle-mounted high-output power supplies. In a typical configuration of this type of secondary battery, an electrode is provided having a configuration in which a material capable of reversibly storing and releasing lithium ions (electrode active material) is retained in an electrically conductive member (electrode current collector). For example, a typical example of an electrode active material used in a positive electrode (positive electrode active material) is an oxide containing lithium and one type or two or more types of transition metal elements as constituent metal elements thereof. In addition, a typical example of a current collector used in a positive electrode (positive electrode current collector) is a sheet-like or foil-like member consisting mainly of aluminum or an aluminum alloy.
An example of a typical method of retaining a positive electrode active material in a positive electrode current collector in the production of a positive electrode having such a configuration consists of coating a paste-like or slurry-like active material layer-forming material, in which a powder of a positive electrode active material and a binder are dispersed in a suitable medium (to be referred to as an active material layer-forming paste), onto a positive electrode current collector, and drying this by passing through a hot air dryer and the like to form a layer containing the positive electrode active material (positive electrode active material layer). The binder contained in the positive electrode active material layer is composed of, for example, a polymer material, and fulfills the role of binding positive electrode active materials contained in the positive electrode active material layer or binding the positive electrode active material layer and the positive electrode current collector. Patent Document 1 is an example of the prior art relating to this type of electrode production.    Patent Document 1: Japanese Patent Application Laid-open No. H11-176423
However, in the production of an electrode as described above, when a mixture layer-forming paste containing an active material and a binder is coated onto a current collector and dried by applying hot air, convection occurs during drying, and since binder in the vicinity of the current collector rises to the surface layer of the paste coating (opposite side of the current collector), the amount of binder in the vicinity of the current collector decreases, thereby resulting in the problem of a decrease in adhesion (adhesive strength) between the current collector and the mixture layer.
In Patent Document 1, a technology is described for enhancing adhesion between a current collector and a mixture layer by providing a binder layer containing a binder between a current collector and an active material layer. In Patent Document 1, the active material layer is layered over this binder layer. The use of this method enhances adhesion between the binder layer and the active material layer, thereby making it possible to prevent interlayer separation.
However, when a binder layer containing a binder (polymer material) is provided between a current collector and an active material layer in the manner of Patent Document 1, since the electrical conductivity of the binder layer is low, there is the possibility of an increase in electrical resistance between the current collector and the active material layer. Since an increase in electrical resistance between the current collector and the active material layer results in an increase in internal resistance of the battery, battery performance of a battery constructed using an electrode having this binder layer can decrease considerably in comparison with batteries in which this binder layer is not formed.